Currently, existing hearing aid analysis technologies are designed to assess the performance of individual electroacoustical components found in or associated with hearing aids. This technology verifies whether the individual electroacoustical components are functioning properly and whether the components maintain their performance within the tolerance standards promulgated by the American National Standard Institute (ANSI). In these testing strategies, simple and highly predictable signals are typically used to evaluate the functioning of the components. For example, sine wave tones are typically used. However, with advances in digital technology and the utilization of sophisticated signal processing strategies, the use of simple predictable signals may not be very closely related to the effect upon sounds which is ultimately perceived by the hearing aid wearer (e.g., speech or music).
Typically, for the successful adaptation of a hearing aid to a given patient, a number of steps are taken. Initially, as indicated above, the hearing aid itself is evaluated to ensure that all of the components are functioning properly. Current technology prescribes a battery of tests to systematically analyze the electroacoustical components of the hearing aid. For example, the microphone and receiver are tested in terms of their frequency response and to determine the level of distortion introduced into test signals. Modem hearing aids also include amplifiers, telecoils, and many other electronic components. Telecoils are inductive devices which are used to receive signals that are not acoustic in origin. Telecoils respond to an electromagnetic field created by, for example, a telephone handset. By the use of a simple switch, the hearing aid wearer is able to activate the telecoils and deactivate the microphone, thereby eliminating problems of feedback, distortion and background noise. The signal from the telephone is transmitted directly, electromagnetically to the hearing aid receiver and an amplified clear signal is provided to the hearing aid wearer. Telecoils can also be used to receive signals created by loop systems imbedded in many public facilities such as churches and theaters. Unfortunately, these tests do not determine whether more sophisticated technology such as dynamic compression, advance noise reduction strategies, and speech cue enhancement are functioning properly.
After the electroacoustical components are tested, the hearing aid is programmed based on manufacturer specifications and a fitting strategy adapted to the needs of the individual hearing aid wearer. Previously gathered audiometric data is used to estimate amplification levels as a function of frequency to make a desired signal audible. In addition, compression levels are set, based again on audiometric data, to ensure that the desired signal remains at a comfortable amplification level.
Next, the fitting strategy is verified using what are referred to as “real ear methods.” A real ear method involves placing a probe tube microphone inside the ear canal of the user while the hearing aid is in place. The test operator then presents sinusoidal signal tones through a speaker, the tones are amplified by the hearing aid and the amplified result is sensed by the probe tube microphone. This confirms that selected frequency ranges are appropriately amplified as desired. In this procedure, no real world signals such as speech are introduced or tested, therefore, no information has been gathered to verify whether some of the more advanced processing techniques of the modern hearing aids are functioning adequately.
Finally, the hearing aid system is put through a validation process. The aim of the validation process is to ensure that the hearing aid components, the programming based on audiometric data, and the verification based on real ear measurements are sufficient to allow the hearing aid wearer to function adequately. Unfortunately, in many cases, this last stage of testing is not completed. Some individuals, particularly younger children, older adults and cognitively impaired individuals, may not be able to adequately cooperate to complete the testing procedure. These validation testing procedures typically include a process in which words or sentences are presented at a normal conversational level in a quiet environment and the hearing aid wearer is requested to repeat the words or sentences played. In some situations, the test is repeated in an environment that includes significant background noise. As can be imagined in this situation, careful calibration of the test signals, whether words or sentences, is very important to the success of the test. Calibration is a continuing and common problem in this field.
While the preferred embodiment of the present invention has been described and tested with respect to speech recognition for the English language, it will be recognized that the present invention is equally applicable to speech recognition in other languages. Given the phonetic, timing and tonal differences of different languages, the present invention may also be utilized to identify hearing aids that are better suited for particular languages based on speech recognition in that language. Similarly, the present invention can not only be used to differentiate the response of different hearing aids, but can also be utilized to evaluate and adjust a single hearing aid for a particular patient in terms of programmable parameters and setting adjustments for that hearing aid.
Examples of current hearing aid testing equipment include the Fonix® line of hearing aid analyzers, the Aurical™ audiodiagnostic and fitting system and the MS40 Hearing Aid Analyzer. U.S. Pat. No. 5,703,797 describes the use of a digital Fourier transform to analyze warbled tones supplied to a hearing aid for test purposes. U.S. Pat. No. 5,729,658 describes a hearing aid evaluation system that generates multiple computer models of processed signal articulation to aid in evaluation and selection of a hearing aid for a given patient. Automated system for hearing aid prescription and patient analysis are described in U.S. Pat. Nos. 5,923,764 and 6,366,863.
PCT Publ. No. WO 99/31937 describes a hearing aid adjustment system that causes a list of pre-selected words to be played for a user with an electronically programmable hearing aid. The user repeats what has been heard to a speech recognition program that has been pre-trained by the hearing aid user. The computer executing the speech recognition program determines which words are correctly identified in response to the spoken words by the hearing aid user. An imputed inverse transform is computed based on pre-knowledge of the frequency content and time and amplitude variation of the pre-selected words. The computed inverse transform is then used to electronically adjust the programmable hearing aid.
While these approaches are adequate for simple testing and adjustment of hearing aids, the hearing aid arts would benefit greatly from the availability of an objective testing technique to improve the evaluation of the effectiveness of hearing aids and particularly the effectiveness of advanced hearing aid technology such as dynamic compression, advanced noise reduction and speech cue enhancement.